To evaluate the association of age at first sexual intercourse with the results of the cervicovaginal cytology. Study Design Observational analytical study about the prevalence of altered cervicovaginal cytology results in women aged between 18 and 34 years from a densely populated area in Brazil, during 10 years. The patients were stratified into 2 categories according to their age at first sexual intercourse (13-16 years and 17-24 years). Results From the total of 2,505,154 exams, 898,921 tests were in accordance with the inclusion criteria. Considering women with 4 years or less from the first sexual intercourse as a reference, those with 5 to 9 years and 10 years or more showed a higher prevalence of high-grade squamous intraepithelial lesions (HSILs). Women with an earlier onset of sexual intercourse (13-16 years) showed higher prevalence ratios for atypical squamous cells (ASC), low-grade squamous intraepithelial lesion (LSIL) and HSIL. The prevalence ratio for HSIL adjusted by age at diagnosis and by age at first sexual intercourse was higher only for women with an earlier onset of sexual intercourse. Conclusions The age of first sexual intercourse could be a variable that might qualify the selection among young women who are really at a higher risk for HSIL.